Birds raise their voice over noisy traffic

Some birds, it's been found, alter their song in response to noisy traffic. This finding follows the recording of bird songs in different locations along Victoria's Mornington Peninsular. Where traffic noise was intense, birds sang at a higher pitch. And bird populations were found to be lower in noisy environments. Kirsten Paris says road surfaces should be chosen that produce lower traffic noise. Matthew Crawford reports.

Transcript

Robyn Williams: Time to turn to something a trifle more tangible, like signing birdies. Here's Matthew Crawford in deepest Victoria.

Matthew Crawford: This noisy roadside environment isn't the best place for me to go about achieving those necessities in life such as finding a mate, warning my friends of danger or begging for food, and that would be especially true if I were a bird.

But if I retreat 50 or so metres from the road I automatically relax the pitch of my voice and it becomes a bit easier to communicate. And that's exactly what Kirsten Parris has observed among some species of Australian birds. She's a research fellow at the University of Melbourne's School of Botany. Kirsten, what was it about the pitch of birdsong that you noticed in your recordings?

Kirsten Parris: I found that at sites where there was a lot of noisy traffic, the birds were singing at a higher pitch or a higher frequency. I did a study with my colleague, Angela Schneider, along the Mornington Peninsula south-east of Melbourne, and we recorded birdsong at around 60 different sites next to roads. Some of those sites were very quiet with hardly any traffic and others were very noisy. We observed that the birds singing at the quiet sites sang lower than the ones singing at the noisy sites.

Matthew Crawford: So how do you actually analyse those recordings to come to those findings?

Kirsten Parris: We made digital recordings which then can be analysed using certain sound programs, and you can identify the frequency that contains the most energy within the signal. So we looked at the lowest tonal note within a song and analysed the dominant frequency of that note.

Matthew Crawford: And which species of birds did you observe, and how did they each cope with the noisy environments?

Kirsten Parris: The two birds that we've got the most data for are the Grey Shrike-thrush and the Grey Fantail. The Grey Shrike-thrush sings quite low, between 1 to 3 kilohertz or 1,000 to 3,000 hertz. And the song of the Grey Shrike-thrush changed noticeably from the quiet sites to the noisy sites. In contrast, the Grey Fantail is a smaller bird which sings at a much higher pitch, around 4 to 5 kilohertz, and we didn't observe a noticeable change in the song of this bird, and we think that's probably because it sings high enough that it's not interfered with by the low frequency traffic noise as much as the other species is.

Matthew Crawford: Here is an example that you've made. This is a simulation, but it demonstrates the average pitch change that you observed. Here's the original:

[birdsong]

And here it is again but shifted up in pitch to the average that Kirsten observed in the noisier areas:

[birdsong]

So, Kirsten, that is quite noticeable. Is that enough for the Grey Shrike-thrush to make itself heard in the noisier places?

Kirsten Parris: Well, it helps a bit, but unfortunately it doesn't compensate fully for the difficulties it has communicating in those noisy areas. So even though the Grey Shrike-thrush is changing its song in noisy conditions, it's not changing it enough to overcome the background noise, and we've seen evidence from our surveys that traffic noise is also impacting on populations of the species. So where it's quiet we're much more likely to find the bird than at sites where it's noisy.

Matthew Crawford: And why should we be worried about the risk of driving birds away from our noisier environments?

Kirsten Parris: Our noisier environments are expanding as cities get larger and larger in Australia and around the world, and also the level of noise we have in our cities is increasing as well because of the numbers of cars, the traffic volumes are going up and up all around the world. So basically what we're doing is leaving less and less space for other species to live. So we've taken away their physical habitats in a lot of cases by constructing cities. There are some species that can still hang on in parts of cities and in roadside habitats, but they now have to contend with increasing levels of noise as well.

Having a diverse range of birds within our cities is not just good for the birds but it's good for people as well because there's evidence from some really interesting research that shows that the mental wellbeing of people, their feelings of wellbeing increase when they can access parklands and other areas that have a diverse range of bird species. So the more birds people could see, the happier they are.

Matthew Crawford: And it's not just about the noise of cars, is it, because car manufacturers these days will say that they're quieter and more environmentally sensitive than ever. What are the other factors about, for instance, traffic, that actually is resulting in an increase in noise?

Kirsten Parris: The level of traffic noise we have is related directly to how many vehicles there are, and that's not just cars but also heavy vehicles like trucks and, in Australia, a lot more of our freight is being transported by road in large trucks rather than by rail these days, so there's an increase in heavy vehicles. Other aspects one could think about include the surface of the road. Certain surfaces are smoother and quieter, and using those could help to reduce levels of traffic noise.

Matthew Crawford: So just in terms of the noise that we are creating in our environments, what other kinds of measures can we do to help?

Kirsten Parris: I think in certain places if there are populations of endangered species of birds that are in the path of new roads, there are very good arguments for not building the road where they are or protecting them from the noise by building sound barriers or other structures. At the moment there is legislation to protect people from certain levels of noise, but there's no legislation to protect non-human animals from noise. So that could be something we could look at in the future.

Robyn Williams: The subtleties of living with animals. Kirsten Parris is at the University of Melbourne and she was with Matthew Crawford.